Superdense coding

After seeing how entanglement can be achieved between two non-interacting parties, we shift our focus to a slightly different application of quantum mechanics in information processing. Listen to Gustavo Amaral (QuTech) explaining Superdense Coding, you will see how it is possible to transmit two classical bits by sending one single qubit.

Prerequisite knowledge

• Multiqubit systems
• Multiqubit gates
• Entanglement
• Measuring multiqubit systems

Further thinking

Which of the following unitaries prepares the following Bell state?

G_i denotes gate G applied to qubit i, and CNOT_ij denotes a CNOT gate with control qubit i and target qubit j.

What state do you get if you apply the Bell preparation circuit to the state |11>?

Solutions

Further reading

For further information on superdense coding see section 2.3 in M. A. Nielsen and I. L. Chuang, Quantum computation and quantum information, 10th anniversary ed. Cambridge ; New York: Cambridge University Press, 2010.
See the original publication of the superdense coding protocol: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.69.2881